The basic principle behind most spectrometers involves the separation of different wavelength channels within an input beam onto different locations of an output plane using some type of dispersive element. The output may be detected using some type of detector array or a charged coupled device (CCD). Because of the scalar nature of the spectrum, such dispersive elements (e.g., gratings and prisms) generally provide a mapping between the different wavelengths and various spatial locations along a line on the detector. For example, for the case of a simple sinusoidal grating, dispersion is obtained across a line in a direction parallel to the grating vector. Thus, in the direction perpendicular to the grating vector, the output beam is almost uniform and does not carry any spectral information. Generally for most applications, a CCD, which is a two-dimensional array of detectors, will be used in the output plane. However, the output in the direction perpendicular to the dispersion direction is almost useless in most conventional implementations.
There are several parameters involved in the design of an efficient spectrometer. Two important performance attributes of a spectrometer are the resolution and spectral operating range of the spectrometer. The resolution of a spectrometer is generally defined as the smallest difference in the wavelengths of two monochromatic input beams that can be resolved at the corresponding outputs at a detector. The operating range of the spectrometer is defined as the maximum range of wavelengths over which the spectrometer can determine the spectrum of the input. While both the resolution and the operating range of any spectrometer depend on several design parameters, it is difficult to maximize both parameters using conventional design techniques.